Aluminum alloy foil

Abstract

To provide an aluminum alloy foil having superior moldability while ensuring the stretch of the foil.SOLUTION: An aluminum alloy foil contains Fe: 0.8 mass% or more and 1.8 mass% or less, Si: 0.01 mass% or more and 0.15 mass% or less, and Cu: 0.001 mass% or more and 0.05 mass% or less, with Mn, one of unavoidable impurities, being limited to 0.01 mass% or less, with the balance being Al and the other unavoidable impurities. When an arithmetic mean roughness before plastic working is R0, an arithmetic mean roughness after plastic working is Ra, and a strain during plastic working is ε, the increase ratio α of surface cracking attributable to plastic working meets the following formula: α=(Ra-R0) / ε≤0.02.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an aluminum alloy foil to be subjected to forming processing. [Background technology]

[0002] Aluminum alloy foils used as packaging materials for food products, lithium-ion batteries, etc. are required to have high formability because they are subjected to large deformations during press forming and other processes. For example, Patent Document 1 specifies the range of components, the grain size of crystal grains, and the area ratio of Cube orientation, thereby improving formability. Furthermore, Patent Document 2 states that the ratios of the diffraction intensities representing the (111) plane, the (100) plane, the (110) plane, and the (311) plane are specified to improve formability. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-115376 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-052158 Summary of the Invention [Problem to be solved by the invention]

[0004] However, conventional aluminum alloy foils do not have sufficient formability. Incidentally, as the plastic processing accompanying the forming of aluminum foil progresses, unevenness occurs on the surface of the material, and in order to obtain good formability, it is necessary to suppress and reduce this unevenness. The present invention has been made in light of the above circumstances, and one of its objects is to provide an aluminum alloy foil having high formability. [Means for solving the problem]

[0005] That is, among the aluminum alloy foils of the present invention, a first embodiment contains Fe: 0.8% by mass or more and 1.8% by mass or less, Si: 0.01% by mass or more and 0.15% by mass or less, Cu: 0.001% by mass or more and 0.05% by mass or less, the inevitable impurity Mn is restricted to 0.01% by mass or less, and the balance is Al and other inevitable impurities, and has a composition in which the arithmetic mean roughness before plastic working is R0 and the arithmetic mean roughness after plastic working is R a When the strain during plastic working is ε, the increase rate α of surface roughness due to plastic working satisfies the following formula: α=(Ra-R0) / ε≦0.02

[0006] Another aspect of the invention of the aluminum alloy foil is characterized in that, in the above-mentioned aspect of the invention, the elongation at angles of 0°, 45° and 90° relative to the rolling direction is 25% or more.

[0007] The contents defined in the present invention will be explained below.

[0008] The reasons for limiting each component in the composition of the aluminum alloy foil of the present invention will be explained below.

[0009] Fe: 0.8% by mass or more and 1.8% by mass or less Fe crystallizes as an Al-Fe intermetallic compound during casting and acts as a recrystallization site during annealing, effectively refining the recrystallized grains. A low Fe content results in a low distribution density of coarse intermetallic compounds, reducing the refining effect and resulting in a non-uniform final grain size distribution. On the other hand, an excessive Fe content saturates or reduces the grain refining effect, significantly increasing the size of the Al-Fe compounds formed during casting, resulting in reduced foil ductility and rollability. For these reasons, the Fe content is limited to a lower limit of 0.8% by mass and an upper limit of 1.8% by mass. For similar reasons, a lower limit of 1.0% by mass and an upper limit of 1.6% by mass are desirable.

[0010] Si: 0.01 mass% or more and 0.15 mass% or less Si crystallizes coarse intermetallic compounds during casting. It is desirable to limit the amount of Si added to prevent the formation of coarse intermetallic compounds. However, if the content is too low, it is necessary to use high-purity metal, which significantly increases manufacturing costs. On the other hand, if the content is excessive, it can lead to coarsening of the compound size and a decrease in distribution density, which can lead to concerns about reduced rollability, elongation, and formability. For this reason, the lower limit of the Si content is set at 0.01% by mass and the upper limit at 0.15% by mass. For the same reason, it is desirable to set the lower limit at 0.01% by mass and the upper limit at 0.08% by mass.

[0011] Cu: 0.001 mass% or more and 0.05 mass% or less Cu is an element that increases the strength of aluminum foil and reduces its elongation. On the other hand, it also has the effect of suppressing excessive work softening during cold rolling, which has been reported for Al-Fe alloys. If the Cu content is too low, the effect of suppressing work softening is low, and if it is too high, elongation is clearly reduced. For this reason, the lower limit of the Cu content is set to 0.001 mass% and the upper limit to 0.05 mass%. For the same reason, it is desirable to set the lower limit to 0.005% and the upper limit to 0.01%.

[0012] Mn: 0.01% by mass or less Mn dissolves in the aluminum matrix as an impurity or forms very fine compounds, which inhibit the recrystallization of aluminum. Trace amounts of manganese can be expected to inhibit work softening, similar to copper, but high contents delay recrystallization during intermediate and final annealing, making it difficult to obtain fine, uniform crystal grains. Therefore, the manganese content is limited to 0.01% or less. For the same reason, a manganese content of 0.005% or less is desirable.

[0013] Increase in surface roughness due to plastic working α When aluminum foil is plastically deformed, unevenness (surface roughness) occurs on the material surface. Surface roughness is considered to be unevenness in thickness, and by suppressing it, it is possible to prevent a decrease in the forming limit. The arithmetic mean roughness before plastic processing is R0, and the arithmetic mean roughness after plastic processing is R a When the plastic strain is ε, the increase rate α of surface roughness due to plastic working satisfies the following formula: α=(R a -R0) / ε≦0.02 If the increase rate α exceeds 0.02, the forming limit decreases.

[0014] Elongation at 0°, 45°, and 90° to the rolling direction is 25% or more The aluminum alloy foil of the present invention preferably satisfies the above elongation characteristics. At any of these angles, high elongation provides high formability. [Effects of the Invention]

[0015] According to the present invention, it is possible to suppress a decrease in the forming limit and obtain excellent formability. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a graph showing the increment of surface roughness (Ra-R0) relative to plastic strain in an example of the present invention. [Figure 2] FIG. 1 is a diagram showing the planar shape of a square punch used in a limit forming height test in an example of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] Hereinafter, an embodiment of the aluminum alloy foil of the present invention will be described. In the production of the aluminum alloy foil of this embodiment, first, an ingot adjusted to a predetermined composition is melted. The ingot, or slab, is subjected to a homogenization treatment, followed by hot rolling and then cold rolling. In the cold rolling, one or more intermediate annealings can be performed as desired. In the final cold rolling after the last intermediate annealing, rolling is performed at a predetermined reduction ratio to obtain an aluminum alloy foil of a predetermined thickness. The aluminum alloy foil after cold rolling is subjected to final annealing to obtain the alloy foil of this embodiment. The aluminum alloy foil of this embodiment can be subjected to forming processing. Each step will be described below.

[0018] Casting: Slab thickness: 600mm to 750mm Casting to obtain ingots can be performed using conventional methods, but it is desirable to set the slab to a specified thickness. The slab thickness affects the cooling rate during casting, and also the size and distribution of the crystallized products and crystal grains that form during casting. Furthermore, different slab thicknesses also affect the rolling ratio to the final foil. It is believed that the refinement and uniformity of the crystal grains after casting contributes to the refinement and uniformity of the foil after final annealing. Furthermore, changes in the rolling ratio due to variations in slab thickness also contribute to the development of texture in the final foil. These crystal grain size and the degree of texture accumulation affect surface roughness, which in turn contributes to formability. For this reason, a slab thickness of 600 mm or more is desirable. However, if the slab thickness exceeds 750 mm, the cooling rate during casting decreases, making it more likely that crystallized deposits and coarsening of the crystal grain size will occur during casting.

[0019] Predetermined composition The aluminum alloy foil has a composition containing Fe: 0.8% by mass or more and 1.8% by mass or less, Si: 0.01% by mass or more and 0.15% by mass or less, Cu: 0.001% by mass or more and 0.05% by mass or less, the inevitable impurity Mn is restricted to 0.01% by mass or less, and the remainder is Al and other inevitable impurities.

[0020] Homogenization: 480℃~540℃ x 8 hours or more The homogenization treatment is intended to eliminate microsegregation in the ingot and adjust the distribution state of intermetallic compounds, and is an important treatment for obtaining a fine and uniform crystal grain structure in the aluminum alloy foil after final annealing. If the homogenization temperature is less than 480° C., the crystal grains will not be sufficiently refined, and if it exceeds 540° C., the crystal grains will become coarse. If the treatment time is less than 8 hours, the homogenization will be insufficient.

[0021] Hot rolling Finishing temperature: 230℃~280℃ When hot-rolling the ingot after homogenization, the finishing temperature is important. Setting the finishing temperature appropriately suppresses recrystallization (giving the hot-rolled sheet a fibrous structure). However, if the finishing temperature exceeds 280°C, recrystallization occurs in some parts of the sheet after hot rolling, making it difficult to obtain an ideal texture in the final product. Furthermore, a non-uniform structure with a mixture of fibrous grains and recrystallized grains contributes to non-uniformity in the crystalline grain structure of the final product, potentially resulting in reduced formability. On the other hand, finishing at a rolling temperature below 230°C requires extremely low temperatures during hot rolling, which could lead to cracks on the sides of the sheet and significantly reduce productivity. For this reason, the finishing temperature for hot rolling should be within the above range.

[0022] : Rolling ratio 99.2% or more It is desirable to set the rolling reduction rate from slab to hot rolling finish at 99.2% or more to break up the crystallized particles formed during casting. In addition, a high rolling reduction rate will result in a fibrous structure after hot rolling.

[0023] cold rolling Hot rolling is followed by cold rolling, which may be interrupted by one or more intermediate anneals. Intermediate annealing: 300-400℃ x 3 hours or more It softens materials that have been hardened by cold rolling (restores rollability), and also promotes the precipitation of Fe, reducing the amount of dissolved Fe. If the intermediate annealing temperature is less than 300°C, there is a risk that recrystallization will not be complete and the grain structure will be non-uniform. Furthermore, if the intermediate annealing temperature is higher than 400°C, the recrystallized grains will coarsen, resulting in a larger final grain size. Furthermore, at higher temperatures, the amount of precipitated Fe decreases and the amount of dissolved Fe increases. A high amount of dissolved Fe suppresses recrystallization during the final annealing, significantly increasing the density of Cu and R orientations. Even if the treatment time is less than 3 hours, there is a risk that recrystallization will be incomplete and Fe precipitation will be insufficient.

[0024] For intermediate annealing, batch annealing is performed in which the coil is placed in a furnace and held there for a certain period of time. There are two methods: continuous annealing (CAL annealing) and rapid heating and cooling of materials using a continuous annealing line (CAL annealing). Either method is acceptable when intermediate annealing is required. For example, in batch annealing, conditions such as 300 to 400°C for 3 hours or more can be adopted, and in CAL annealing, conditions such as a temperature rise rate of 100 to 250°C / sec, a heating temperature of 420 to 470°C, no holding time or a holding time of 5 seconds or less, and a cooling rate of 20 to 200°C / sec can be adopted. However, in this embodiment, the presence or absence of intermediate annealing, and the conditions when intermediate annealing is performed, are not limited to specific ones.

[0025] Final cold rolling: reduction rate of 95% or more Because grains are refined during cold rolling (grain subdivision), the higher the final cold-rolling reduction from intermediate annealing to final thickness, the finer the grains. Furthermore, the higher the cold-rolling reduction, the more the Cu and R orientations can be developed. Therefore, a higher final cold-rolling reduction is desirable; specifically, a final cold-rolling reduction of 95% or more is desirable. However, if the final cold-rolling reduction is less than 95%, the recrystallized grain size after final annealing becomes coarse and nonuniform, resulting in worse surface roughness and making it difficult to achieve high ductility and therefore high formability.

[0026] Thickness after final cold rolling A desired thickness can be achieved by final cold rolling. In this embodiment, the thickness is not particularly limited, but a thickness of 10 to 40 μm can be shown, for example.

[0027] Final annealing: 250℃~350℃ x 10 hours or more Final annealing is performed to completely soften the foil after final cold rolling. Final annealing after foil rolling may be performed at, for example, 250°C to 350°C. If the final annealing temperature is too low, softening is insufficient. If the temperature exceeds 350°C, problems such as deformation of the foil and reduced economic efficiency arise. If the final annealing time is less than 10 hours, the effect of the final annealing is insufficient.

[0028] In the aluminum alloy foil of the embodiment, the increase rate α{(Ra−R0) / ε} of surface roughness due to plastic working is 0.02 or less. When the arithmetic mean roughness before plastic working is R0, the arithmetic mean roughness after plastic working is Ra, and the strain during plastic working is ε, the increase rate α of surface roughness due to plastic working is 0.02 or less. The strain (ε) in the calculation formula represents plastic strain and is calculated according to the deformation mode, such as tension, compression, shear, torsion, etc. For example, ε due to uniaxial tension is calculated as follows: First, before the tensile test, two lines are drawn vertically in the center of the test piece and the distance between them (l0) is measured. After deformation, the distance between the two lines (l1) is measured again and calculated as ε = ln(l1 / l1). The above-mentioned requirements can be achieved by controlling the slab thickness in the manufacturing process to 600 mm to 750 mm, and by controlling the size and distribution of crystallized particles and crystal grains generated during casting, as well as the rolling ratio up to the final foil, thereby optimizing the crystal grain size and texture in the final foil.

[0029] Elongation at 0°, 45°, and 90° relative to the rolling direction is 25% or more The aluminum alloy foil of the embodiment preferably has elongation of 25% or more at angles of 0°, 45°, and 90° relative to the rolling direction. The elongation of the aluminum alloy foil of this embodiment does not necessarily have to satisfy this condition, but it is preferable that it does, and it is even more preferable that the elongation in the above three directions is 30% or more. The above elongation characteristics can be obtained by appropriately controlling the slab thickness and rolling ratio in the manufacturing process, similar to the surface roughness described above.

[0030] In this embodiment, it is desirable that the following characteristics be further provided. For crystal grains surrounded by high-angle grain boundaries with a misorientation of 15° or more, the average grain size is 15 μm or less, and the maximum grain size / average grain size is 3.5 or less. By suppressing the surface roughness of foil that occurs during plastic processing, improvements in elongation and formability can be expected. One of the factors that influence this surface roughness is the crystal grain size, and to suppress surface roughness, it is desirable to have an average crystal grain size of 15 μm or less. Furthermore, if the crystal grain size distribution is uneven, it is expected that localized deformation will occur more easily, resulting in reduced elongation. Therefore, high formability can be achieved not only by keeping the average crystal grain size 15 μm or less, but also by ensuring that the maximum grain size / average grain size is ≦3.5. However, regarding the crystal orientation density, when the Cu orientation is 50 or more, the average crystal grain size may be 25 μm or less. The above properties can be obtained by appropriately controlling the slab thickness and rolling ratio in the manufacturing process, similar to the surface roughness and elongation mentioned above.

[0031] Cube orientation density 6 or less and Cu orientation density 30 or more Texture also affects the surface roughness of foil. Surface roughness occurs frequently near grain boundaries and is therefore related to the deformation and nonuniformity of individual grains. If the crystal orientation is relatively uniform, the deformation and rotation of the crystal grains during deformation are similar. However, if the orientation varies greatly, plastic deformation causes nonuniform deformation and rotation of each crystal grain, which leads to the development of surface roughness. Therefore, accumulating crystal orientations contributes to the suppression of surface roughness. Because foils are thin, the rolling ratio during their manufacturing process is relatively high, making it easy for rolling texture to develop. However, if Cube orientation also develops at the same time, the variation in crystal orientation increases, making this unsuitable for suppressing surface roughness. Therefore, it is desirable for the Cube orientation density to be 6 or less and the Cu orientation density to be 30 or more. However, if the average crystal grain size is 6 μm or less, the Cu orientation density may be 15 or more. The above Cube orientation density and Cu orientation density can be obtained by setting the final cold rolling reduction rate to 95% or more in the manufacturing process. [Example]

[0032] Examples of the present invention will be described below. The aluminum alloys shown in Table 1 (the balance being Al and other unavoidable impurities) were melted by a conventional method to obtain slabs with the thicknesses shown in Table 2. The slabs were subjected to a homogenization treatment at 500°C for 8 hours or more. The slabs after the homogenization treatment were hot rolled to a finished thickness of 5 mm by the hot rolling method shown in Table 2, and the hot rolling finishing temperature was 235°C to 284°C.

[0033] The hot-rolled material was then cold-rolled. During cold rolling, all the materials except for test material No. 10 were subjected to intermediate annealing when the plate thickness reached 2.8 mm (cold rolling reduction of 44.4%). The intermediate annealing was carried out in a batch furnace at 360°C for 3 hours. Thereafter, final cold rolling was carried out until the finished thickness reached 40 μm. The reduction ratio of the final cold rolling was 98.6%. Test material No. 10 was rolled to the finished thickness without intermediate annealing. Therefore, the final cold rolling reduction was 99.2%. The aluminum alloy foil after the cold rolling was subjected to final annealing under the conditions of 300°C x 20 hours.

[0034] The obtained test materials were evaluated for the following items, and the evaluation results are shown in Table 3.

[0035] Growth rate The elongation was measured by a tensile test in accordance with JIS Z2241. JIS No. 5 test pieces were prepared so that the elongation could be measured in the directions of 0°, 45°, and 90° relative to the rolling direction. The test was carried out using a universal tensile tester (Shimadzu Corporation, AGS-X 10kN) at a tensile speed of 5mm / min. The elongation percentage was calculated as follows: First, before the test, two lines were marked perpendicular to the longitudinal center of the test piece at an interval of 50 mm, which is the gauge length. After the test, the fracture surfaces of the aluminum alloy foil were butted together to measure the distance between the marks, and the gauge length (50 mm) was subtracted from this to obtain the elongation amount (mm), which was then divided by the gauge length (50 mm) to obtain the elongation percentage (%).

[0036] Surface roughness measurement The plastic working in this example was carried out by a tensile test. The tensile test was carried out in the same manner as in the elongation measurement in the previous section, using a JIS No. 5 test piece and applying tensile strain using the universal tensile tester. The surface roughness of the test materials was measured in accordance with JIS B0601:2001. The actual measurements were performed using a confocal laser microscope (Keyence, VK-X100) and an analysis application (Keyence, VK-H1XA). The observation magnification was 500x, the field of view size was 1000 x 500 μm, and the measurement location was the center of the width and length of the JIS No. 5 test piece. The data scanned by the laser microscope was subjected to noise removal and tilt correction, and the surface roughness was measured. For noise removal, the noise detection level was set to "Normal," and for tilt correction, the correction method was selected to "Surface tilt correction (profile)." The surface roughness parameter was calculated based on JIS B0601:2001 using the arithmetic mean roughness of the surface roughness.

[0037] The procedure for continuous observation is described below. First, the surface properties of the test piece before the test are observed using a confocal laser microscope. Then, a tensile test is performed. The test is stopped at any point during plastic deformation, and the surface properties after plastic deformation are observed again (surface roughness measurement). After the observation, the same test piece is further processed, and the test is stopped during plastic deformation to observe the surface properties (surface roughness measurement). This procedure is repeated multiple times (at least three times or more), and the surface shape is measured at different arbitrary strain levels. The plastic strain obtained in each measurement and the change in arithmetic mean roughness (R a -R0) was plotted and an approximate straight line was drawn using the least squares method to create a graph of the change in surface roughness versus plastic strain, as shown in Figure 1, and the increase rate α of surface roughness was calculated from the slope of the approximate straight line.

[0038] Grain size After electrolytic polishing the foil surface, crystal orientation analysis was performed using a scanning electron microscope (SEM) with backbone diffraction (EBSD). Grain boundaries with a misorientation of 15° or more between grains were defined as high angle grain boundaries (HAGBs), and the size of the grains surrounded by HAGBs was measured. Three fields of view, each 90 x 180 μm in size, were measured at 900x magnification, and the average grain size and the large grain size / average grain size ratio were calculated. The grain size of each grain was calculated using the equivalent circle diameter, and the average grain size was calculated using the EBSD area method (average by area fraction method). The analysis was performed using OIM Analysis from TSL Solutions. The results are shown in Table 3 as average crystal grain size and grain size ratio.

[0039] crystal orientation density Cube orientation is {001} <100> , Cu orientation is {112} <111> The orientation density of each crystal was evaluated by measuring the incomplete pole figures of {111}, {200}, and {220} using X-ray diffraction, and calculating the three-dimensional orientation distribution function (ODF) using the results. The results are shown in Table 3 as Cube orientation density and Cu orientation density.

[0040] Square tube overhang height The square tube overhang height was evaluated in a square tube forming test. The test was performed using a universal sheet metal forming tester (ERICHSEN Model 142 / 20) with a 40 μm thick aluminum foil and a square punch (side length L = 37 mm, corner chamfer diameter R = 4.5 mm) as shown in Figure 2. The test conditions were a wrinkle suppression force of 10 kN, a punch rising speed (forming speed) scale of 1, and mineral oil applied as a lubricant to one side of the foil (the side that the punch contacts). The foil was formed by the punch rising from the bottom of the device. The maximum punch rise height that could be formed without cracks or pinholes after three consecutive forming runs was defined as the square tube overhang height (mm) of the material. The punch height was varied in 0.5 mm increments. The measurement results are shown in Table 3.

[0041] As shown in the table, the examples of the present invention have a larger rectangular tube overhang height and superior formability compared to the comparative examples. In contrast, comparative examples Nos. 11 to 17, in which either or both of the composition and the surface roughness increase rate α due to plastic working are outside the range of the present invention, have a smaller rectangular tube overhang height and inferior formability.

[0042] [Table 1]

[0043] [Table 2]

[0044] [Table 3]

Claims

1. The steel sheet contains Fe: 0.8% by mass or more and 1.8% by mass or less, Si: 0.01% by mass or more and 0.15% by mass or less, Cu: 0.001% by mass or more and 0.05% by mass or less, the inevitable impurity Mn is restricted to 0.01% by mass or less, and the balance is Al and other inevitable impurities, and has a composition in which the arithmetic mean roughness before plastic working is R ０ , the arithmetic mean roughness after plastic working is R ａ 2. An aluminum alloy foil characterized in that, when the strain during plastic working is ε, the increase rate α of surface roughness due to plastic working satisfies the following formula: a=(R) ａ -R ０ ) / ε≦0.02

2. 2. The aluminum alloy foil according to claim 1, wherein the elongation at angles of 0°, 45°, and 90° relative to the rolling direction is 25% or more.

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